class Person:
    def __init__(self, name, age):
        self.__name = name
        self.__age = age

    def get_info(self):
        return f"姓名: {self.__name}, 年龄: {self.__age}"

class Student(Person):
    def __init__(self, name, age, student_id, score):
        super().__init__(name, age)
        self.__student_id = student_id
        self.__score = score

    def get_info(self):
        return f"{super().get_info()}, 学号: {self.__student_id}, 成绩: {self.__score}"

    def get_grade(self):
        if self.__score >= 90:
            return 'A'
        elif self.__score >= 80:
            return 'B'
        elif self.__score >= 70:
            return 'C'
        elif self.__score >= 60:
            return 'D'
        else:
            return 'F'

class Teacher(Person):
    def __init__(self, name, age, course):
        super().__init__(name, age)
        self.course = course

    def get_info(self):
        return f"{super().get_info()}, 教授课程: {self.course}"

    def teach(self):
        return f"{self._Person__name}正在教授{self.course}"

def print_person_info(person):
    print(person.get_info())

# 测试代码
if __name__ == "__main__":
    student = Student("张三", 20, "S1001", 85)
    teacher = Teacher("李四", 35, "Python编程")

    print_person_info(student)
    print(f"学生等级: {student.get_grade()}")
    print_person_info(teacher)
    print(teacher.teach())    